Microgrids are local versions of the centralized electricity system that provide cheap and reliable power in remote areas. Instead of having each household produce their own electricity, microgrids connect several buildings to a single photovoltaic array. This collective approach makes it increasingly cheap to add a load as the installation increases in size. Therefore, for large installations these systems have significant advantages over normal off-grid configurations. While microgrids have essentially the same components as other solar panel systems, the way they are organized is fundamentally different.
Components of a Microgrid
Panels
Solar panels use sunlight to produce electricity. This can be achieved using any of of the three photovoltaic technologies: thin film, monocrystalline or polycrystalline.
Crystalline
- Both types of crystalline panels are more widely used than thin film. They are rigid, efficient (≈18%) and must be mounted. Monocrystalline panels are higher quality and more expensive than polycrystalline panels.
Thin Film
- Thin film cells are flexible and cheaper than crystalline panels. They come on large sheets that are rolled and attached onto a surface during installation. Unfortunately, thin film cells have low efficiency (≈10%). So if you choose to use thin film cells you will have to dedicate much more space to electricity production.
To display the differences between thin film and crystalline panels let's look at two solar products: the Suniva 315w Solar Panel and the Xunlight 97w Solar Panel. The Suniva is a crystalline module and is rated 218w higher than the thin film Xunlight panel. In addition, for a required energy output in any given region the Xunlight panels will have to take up about three times as much space. However the crystalline module costs over $100 more than the thin film modules without taking into consideration panel mounts and thin film technology is more efficient in cloudy conditions.
A microgrid will naturally require many more solar panels than isolated systems that power a single household. However the price per watt of a microgrid is generally lower due to economies of scale. When designing a microgrid engineers can choose an ideal location to put their centralized solar plant. This leads to lower costs and higher output than if a group of isolated off-grid systems were used.
Mounting
Solar module mounting can play a large role in increasing the output of your system (for crystalline panels). Microgrid and utility scale solar plants can be mounted on pole mounts or ground mounts. Where pole mounts organize panels vertically, ground mounts place them side by side on racks. If space is not an issue, it is cheaper to use ground mounts. However, pole mounts are still a very effective way to mount your solar panels, especially in more constraining areas.
The most expensive way to mount solar panels is roof racking. Unfortunately this is the most common racking for solar homes, especially in urban areas due to lack of space. By collaborating with each other, a community can mount their panels in a more efficient way. As previously explained this leads to lower cost.
Inverters
There are two kinds of current: alternating (AC) and direct (DC). Inverters transform DC current from solar panels into AC current. This is an important step as many devices can only be run on AC current. Usually, solar installations use a single central inverter to convert electricity. The downside of this setup is that if just one panel is in a shaded area, it will drop the performance of all other panels. Micro-inverters, the alternative to central inverters, do not have this problem but complicate wiring and increase installation costs for large scale projects such as microgrids. This is one of the downsides of a microgrid. Since it operates on a different level from individual systems, it cannot realistically install a micro-inverter on each panel.
Inverters are designed with a maximum power rating. When choosing an inverter you must therefore find the peak wattage of you system. Take the following example:
Solar panels power a microgrid of 4 buildings. Each building has five 60 watt lightbulbs and two 300 watt desktop computer. The inverter size is (60 x 5 + 2 x 300) x 4 = 3 600 watts.
Charge Controller
Charge controllers make sure that the electricity charging your batteries is at the right voltage. Without these devices battery banks would quickly be ruined. For large scale solar installations such as microgrids, a maximum power point tracking (MPPT) charge controller is crucial. These charge controllers, though more expensive, have huge efficiency benefits over their competitors. Essentially, MPPT controllers convert high DC voltage from the panels to a low charging voltage. Power losses are minimized by constantly optimizing the conversion.
You can find lots of charge controller examples online. A microgrid will require a fairly large charge controller such as the Flex Max 80 MPPT charge controller.
Battery Bank
Since solar panels are only in direct sunlight for a fraction of the day, electricity must be stored during peak hours so that it can be used later. For a microgrid the best option is to use a single large battery bank that can power the grid for around 5 days without recharging. While there are many different types of battery chemistry (NiCad, NiFe, Li+,... ) to choose from, most solar storage systems use lead-acid batteries.
Flooded lead-acid batteries (FLA) are the most popular of the lead acid batteries due to their low price. Unlike valve-regulated batteries (VRLA) they require regular maintenance. If you cannot care and feed your batteries consistently then AGM batteries are the best VRLA cells to choose. They require practically no maintenance, are completely leak proof, can discharge at a high rate, and can be stored on their sides. Though they provide the best durability and convenience, AGM batteries are also the most expensive lead-acid batteries.
Components of a Microgrid
Panels
Solar panels use sunlight to produce electricity. This can be achieved using any of of the three photovoltaic technologies: thin film, monocrystalline or polycrystalline.
Crystalline
- Both types of crystalline panels are more widely used than thin film. They are rigid, efficient (≈18%) and must be mounted. Monocrystalline panels are higher quality and more expensive than polycrystalline panels.
Thin Film
- Thin film cells are flexible and cheaper than crystalline panels. They come on large sheets that are rolled and attached onto a surface during installation. Unfortunately, thin film cells have low efficiency (≈10%). So if you choose to use thin film cells you will have to dedicate much more space to electricity production.
To display the differences between thin film and crystalline panels let's look at two solar products: the Suniva 315w Solar Panel and the Xunlight 97w Solar Panel. The Suniva is a crystalline module and is rated 218w higher than the thin film Xunlight panel. In addition, for a required energy output in any given region the Xunlight panels will have to take up about three times as much space. However the crystalline module costs over $100 more than the thin film modules without taking into consideration panel mounts and thin film technology is more efficient in cloudy conditions.
A microgrid will naturally require many more solar panels than isolated systems that power a single household. However the price per watt of a microgrid is generally lower due to economies of scale. When designing a microgrid engineers can choose an ideal location to put their centralized solar plant. This leads to lower costs and higher output than if a group of isolated off-grid systems were used.
Mounting
Solar module mounting can play a large role in increasing the output of your system (for crystalline panels). Microgrid and utility scale solar plants can be mounted on pole mounts or ground mounts. Where pole mounts organize panels vertically, ground mounts place them side by side on racks. If space is not an issue, it is cheaper to use ground mounts. However, pole mounts are still a very effective way to mount your solar panels, especially in more constraining areas.
The most expensive way to mount solar panels is roof racking. Unfortunately this is the most common racking for solar homes, especially in urban areas due to lack of space. By collaborating with each other, a community can mount their panels in a more efficient way. As previously explained this leads to lower cost.
Inverters
There are two kinds of current: alternating (AC) and direct (DC). Inverters transform DC current from solar panels into AC current. This is an important step as many devices can only be run on AC current. Usually, solar installations use a single central inverter to convert electricity. The downside of this setup is that if just one panel is in a shaded area, it will drop the performance of all other panels. Micro-inverters, the alternative to central inverters, do not have this problem but complicate wiring and increase installation costs for large scale projects such as microgrids. This is one of the downsides of a microgrid. Since it operates on a different level from individual systems, it cannot realistically install a micro-inverter on each panel.
Inverters are designed with a maximum power rating. When choosing an inverter you must therefore find the peak wattage of you system. Take the following example:
Solar panels power a microgrid of 4 buildings. Each building has five 60 watt lightbulbs and two 300 watt desktop computer. The inverter size is (60 x 5 + 2 x 300) x 4 = 3 600 watts.
Charge Controller
Charge controllers make sure that the electricity charging your batteries is at the right voltage. Without these devices battery banks would quickly be ruined. For large scale solar installations such as microgrids, a maximum power point tracking (MPPT) charge controller is crucial. These charge controllers, though more expensive, have huge efficiency benefits over their competitors. Essentially, MPPT controllers convert high DC voltage from the panels to a low charging voltage. Power losses are minimized by constantly optimizing the conversion.
You can find lots of charge controller examples online. A microgrid will require a fairly large charge controller such as the Flex Max 80 MPPT charge controller.
Battery Bank
Since solar panels are only in direct sunlight for a fraction of the day, electricity must be stored during peak hours so that it can be used later. For a microgrid the best option is to use a single large battery bank that can power the grid for around 5 days without recharging. While there are many different types of battery chemistry (NiCad, NiFe, Li+,... ) to choose from, most solar storage systems use lead-acid batteries.
Flooded lead-acid batteries (FLA) are the most popular of the lead acid batteries due to their low price. Unlike valve-regulated batteries (VRLA) they require regular maintenance. If you cannot care and feed your batteries consistently then AGM batteries are the best VRLA cells to choose. They require practically no maintenance, are completely leak proof, can discharge at a high rate, and can be stored on their sides. Though they provide the best durability and convenience, AGM batteries are also the most expensive lead-acid batteries.
Solar technology is becoming increasing important in the global race to clean energy. If you are interested in more information on solar microgrids or are looking for more solar policy and technology articles, please visit http://www.solartown.com/learning. In addition, if you are in the process of joining the sustainable energy movement, you can find everything you need to get off of fossil fuels at this online store: http://www.solartown.com/store/catalog/
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